Tests ethics, but not initially (5)
I believe the answer is:
orals
'tests' is the definition.
(oral is a kind of test)
'ethics but not initially' is the wordplay.
'ethics' becomes 'morals' (synonyms).
'but not initially' means to remove the first letter.
'morals' with its initial letter taken off is 'ORALS'.
(Other definitions for orals that I've seen before include "Spoken exams" , "Tests" .)